Signal receiving apparatus, signal receiving method and signal receiving program

ABSTRACT

A signal receiving apparatus for receiving signals is provided. The signal receiving apparatus includes a correlation-value computation section configured to sequentially compute a correlation value representing a correlation between the received signal and a series of known symbols while sliding the series of known symbols for every symbol included in the received signal, a maximum-value detection section configured to detect a largest correlation value among the correlation values computed by the correlation-value computation section for one frame of the received signal, and a correlation-value storage section configured to store each of the correlation values at one of a predetermined number of storage locations, before and after the largest correlation value is detected by the maximum-value detection section.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent ApplicationJP 2008-12970 filed in the Japan Patent Office on Apr. 23, 2008, theentire contents of which is incorporated herein by reference.

BACKGROUND

Generally, in a radio technology such as a technology underlying digitalcommunications or a technology underlying digital broadcastings, asignal transmitted by a signal transmitting apparatus through a varietyof transmission lines is received by a signal receiving apparatus.Typical examples of the signal transmitting apparatus are a broadcastingapparatus of a broadcasting station, a portable terminal and a relaystation whereas typical examples of the signal receiving apparatus are aTV receiver, a portable terminal and a relay station. In a multipathenvironment in which a signal is transmitted by a signal transmittingapparatus through a variety of transmission lines to a signal receivingapparatus, the signal to be received by the signal receiving apparatusincludes reflected waves and echos as described below.

For example, when a signal transmitted from a signal transmittingantenna connected to a signal transmitting apparatus 11 is received by asignal receiving antenna connected to a signal receiving apparatus 12,the signal receiving apparatus 12 actually receives a principal wavedirectly transmitted by the signal transmitting apparatus 11 and a wavereflected by the building 13 or the like to appear as a delayed wavedelayed by a building 13.

Thus, a signal actually received by the signal receiving apparatus 12 isa compound wave including the principal wave and the delayed wave asdescribed above. That is to say, a signal actually received by thesignal receiving apparatus 12 is a distorted wave. Thus, the quality ofa communication carried out in a multipath environment deteriorates.Therefore, in order to improve the quality of a communication carriedout in a multipath environment, it is necessary to grasp characteristicsof the multipath environment. Generally determined by the communicationenvironment, the characteristics of the multipath environment includethe transmission distance of each of a plurality of transmission linescomposing the communication environment and the reflectioncharacteristic of each of the transmission lines. In the followingdescription, the characteristics of a multipath environment are properlyreferred to as a channel profile.

In a process of estimating a channel profile, a synchronization signalinserted into a data frame of a transmitted/received signal is used. Thesynchronization signal is a series of known symbols. The signalreceiving apparatus 12 has also registered the series of known symbolsin advance. In the following description, the symbol series insertedinto a received signal is also referred to as the symbol series of thereceived signal whereas the symbol series registered in the signalreceiving apparatus 12 in advance is also referred to as the symbolseries of the synchronization signal. The signal receiving apparatus 12computes the correlation value between the synchronization signalinserted into the principal wave of the received signal and theregistered series of known symbols, estimating a channel profile bymaking use of the computation result which is referred to hereafter ascorrelation data.

As an example, FIG. 2 is given as a plurality of diagrams referred to indescription of a typical channel profile estimated from a signalreceived by the signal receiving apparatus 12 in a multipathenvironment. The horizontal axis of the diagram of FIG. 2 represents thelapse of time t. In this case, the time t lapses in the left-to-rightdirection. Each of arrows erected in the upward direction represents themagnitude (or the level) of a correlation value.

As shown in the diagram of FIG. 2A, the signal received by the signalreceiving apparatus 12 includes a principal wave and a post-echo. Asshown in the diagram of FIG. 2B, on the other hand, the signal receivedby the signal receiving apparatus 12 includes a principal wave and apre-echo.

By acquiring such a channel profile, the signal receiving apparatus 12is capable of grasping the characteristics of a transmission linethrough which the signal received by the signal receiving apparatus 12has been transmitted by the signal transmitting apparatus 11. Forexample, the signal receiving apparatus 12 is capable of graspinginformation used for determining whether or not the signal received bythe signal receiving apparatus 12 has been transmitted by the signaltransmitting apparatus 11 through a transmission line which generates apost-echo or a pre-echo. Thus, when carrying out a communication in amultipath environment, by performing equalization processing based onthe channel profile of the multipath environment, it is possible toacquire the basic waveform from a distorted waveform. That is to say,the waveform of only the principal wave can be obtained. Thus, thequality of the communication can be improved.

Next, processing to estimate a channel profile is explained by referringto a diagram of FIG. 3.

For example, for every data frame having a frame length determined inadvance, the signal transmitting apparatus 11 transmits a signalincluding a synchronization signal inserted into the head of the dataframe to the signal receiving apparatus 12 in a multipath environment.In this case, the signal receiving apparatus 12 actually receives acompound signal including the principal wave of the original signal anda wave delayed due to effects of the multipath environment. The signalreceiving apparatus 12 has registered the synchronization signalinserted into the signal received from the signal transmitting apparatus11 as a series of known symbols in advance. The signal receivingapparatus 12 computes the correlation value representing a correlationbetween the synchronization signal inserted into a received signal andthe registered series of known symbols from time to time while slidingthe symbol series of the synchronization signal over the symbol seriesof the received signal.

In the case of a received signal including a principal wave and adelayed wave as described above, in a channel profile found on the basisof correlation data representing computed correlation values, acorrelation value computed with a timing coincident with thesynchronization-signal of the principal wave is the largest value and acorrelation value computed with a timing coincident with thesynchronization signal of the delayed wave is the second largest value.A correlation value computed with a timing other than the timingcoincident with the synchronization signal of the principal wave and thetiming coincident with the synchronization signal of the delayed wave isrelatively small.

As shown in a diagram of FIG. 4, the signal receiving apparatus 12compares the correlation value computed from time to time with acorrelation threshold value th determined in advance and stores thecorrelation value in a memory. Strictly speaking, if the correlationvalue is found equal to or greater than the correlation threshold valueth for the first time, the signal receiving apparatus 12 starts anoperation to store correlation values in a memory. The memory has Nstorage locations which are given addresses 0 to (N−1) respectively. Thefirst correlation value found equal to or greater than the correlationthreshold value th for the first time is stored at a storage locationwith an address of 0. In this case, the subsequent correlation valuesfollowing the first correlation value are stored at the storagelocations with addresses of 1 to (N−1).

If the received signal includes a post-echo for example, when theprincipal wave of the received signal is detected, the signal receivingapparatus 12 starts an operation to store correlation values in thememory shown at the bottom of the diagram of FIG. 4. The correlationvalue computed at the detection time of the principal wave is stored atan address of 0 in the memory as shown by a hatched block on the leftend of the memory. Detection of the post-echo is delayed from thedetection of the principal wave by a delay time. If the delay time isshorter than a period having a length corresponding to the N storagelocations of the memory, the correlation value computed at the detectiontime of the post-echo is stored in the memory as shown by a hatchedblock in the middle of the memory. The computed correlation valuesstored in the memory having a size N storage locations as correlationvalues including the correlation value of the principal wave and thecorrelation value of the post-echo are referred to as correlation datafrom which a channel profile is estimated.

If the process of setting the correlation threshold value th to becompared with the computed correlation values is not carried outproperly, however, a proper channel profile cannot be acquired, forexample, from the correlation data including the correlation value ofthe principal wave and the correlation value of the post-echo as shownin the diagram of FIG. 4.

FIG. 5 is a diagram showing a typical case in which the correlationthreshold value th is set at a level higher than a proper one. In thiscase, the correlation value of the principal wave is computed, beingcompared with the correlation threshold value th and an operation tostore computed correlation values in the memory is started. Even if thereceived signal includes a pre-echo leading ahead of the principal wave,however, the computed correlation value of the pre-echo is not stored inthe memory.

In order to allow the computed correlation value of the pre-echo to bedetected and stored in the memory, on the other hand, the correlationthreshold value th is set at a low level. FIG. 6 is a diagram showing atypical case in which the correlation threshold value th is set at alevel lower than a proper one. In this case, the correlation valuecomputed for a noise to appear as a correlation value higher than thecorrelation threshold value th is detected and an operation to storecomputed correlation values in the memory is started with an operationto store the correlation value computed for the noise. As shown in thediagram of FIG. 6, even though the computed correlation values ofpre-echos and the principal wave can be stored in the memory, thecomputed correlation value of a post-echo cannot because the pre-echo isdetected at a time beyond a period corresponding to the N storagelocations which form the size of the memory.

In the typical cases described above by referring to the diagrams ofFIGS. 5 and 6, it is impossible to obtain correlation data including therequired correlation value of a post-echo or a pre-echo albeit includingthe correlation value of the principal wave. Thus, a proper channelprofile cannot be estimated.

In addition, Japanese Patent Laid-open No. 2004-343542 describes acommunication terminal in which an averaged-correlation-value profile isfound by averaging the values of correlations between a received signaland a reference signal in order to detect a multipath in radiotransmission lines.

As described above, a proper channel profile cannot be estimated fromacquired correlation data in some cases.

SUMMARY

The present disclosure relates to a signal receiving apparatus, a signalreceiving method adopted by the signal receiving apparatus and a signalreceiving program implementing the signal receiving method. Moreparticularly, the present application relates to a signal receivingapparatus capable of acquiring a proper channel profile, a signalreceiving method adopted by the signal receiving apparatus and a signalreceiving program implementing the signal receiving method.

Addressing the problems described above, a signal receiving apparatuscapable of acquiring a proper channel profile is described below.

According to an embodiment there is provided a signal receivingapparatus for receiving signals, the signal receiving apparatusincluding:

a correlation-value computation section configured to sequentiallycompute a correlation value representing a correlation between thereceived signal and a series of known symbols while sliding the seriesof known symbols for every symbol included in the received signal;

a maximum-value detection section configured to detect a largestcorrelation value among the correlation values computed by thecorrelation-value computation section for one frame of the receivedsignal; and

a correlation-value storage section configured to store each of thecorrelation values at one of storage locations, the number of which isdetermined in advance, before and after the largest correlation value isdetected by the maximum-value detection section.

According to another embodiment there is provided a signal receivingmethod for receiving a signal, the signal receiving method including thesteps of:

sequentially computing a correlation value representing a correlationbetween the received signal and a series of known symbols while slidingthe series of known symbols for every symbol included in the receivedsignal;

detecting a largest correlation value among the correlation valuescomputed at the correlation-value computation step for one frame of thereceived signal; and

storing each of the correlation values computed at the correlation-valuecomputation step at one of storage locations, the number of which isdetermined in advance, before and after the largest correlation value isdetected at the maximum-value detection step.

According to yet another embodiment there is provided a signal receivingprogram to be executed by a computer embedded in a signal receivingapparatus for receiving signals to carry out processing including thesteps of:

computing a correlation value representing a correlation between thereceived signal and a series of known symbols while sliding the seriesof known symbols for every symbol included in the received signal;

detecting a largest correlation value among the correlation valuescomputed in the correlation-value computation process for one frame ofthe received signal; and

storing each of the correlation values computed in the correlation-valuecomputation process at one of storage locations, the number of which isdetermined in advance, before and after the largest correlation value isdetected in the maximum-value detection process.

In accordance with the embodiments, a process is carried out tosequentially compute a correlation value representing a correlationbetween a received signal and a series of known symbol while sliding theseries of known symbols for every symbol included in the receivedsignal. Then, a process is carried out to detect a largest correlationvalue among the correlation values computed for one frame of thereceived signal. Finally, a process is carried out to store correlationvalues, the number of which is determined in advance, as correlationvalues computed before and after the largest correlation value isdetected.

In accordance with the embodiments, a proper channel profile can beacquired.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an explanatory diagram showing a multipath environment;

FIG. 2A is a diagram showing a principal wave and a post-echo;

FIG. 2B is a diagram showing a principal wave and a pre-echo;

FIG. 3 is an explanatory diagram to be referred to in description of aprocess to estimate a channel profile;

FIG. 4 is a diagram showing a storage image of correlation values storedin a memory as correlation data to be used for estimating a channelprofile;

FIG. 5 is a diagram showing a storage image of correlation values storedin a memory as correlation data to be used for estimating a channelprofile;

FIG. 6 is a diagram showing a storage image of correlation values storedin a memory as correlation data to be used for estimating a channelprofile;

FIG. 7 is a block diagram showing a typical configuration of a signalreceiving apparatus according to the embodiment;

FIG. 8 shows a flowchart representing threshold-value comparisonprocessing and correlation-data storage processing which are carried outby the signal receiving apparatus;

FIG. 9 is a diagram showing a storage image in a memory inthreshold-value comparison processing;

FIG. 10A is a diagram showing a storage image of the N storage locationsof the memory in which the address Address_m used for storing thecorrelation value P of the principal wave is in the upper half of the Nstorage locations of the memory, that is, m≦N/2;

FIG. 10B is a diagram showing a storage image of the N storage locationsof the memory in which the address Address_m used for storing thecorrelation value P of the principal wave is in the lower half of the Nstorage locations of the memory, that is, m>N/2;

FIG. 11 shows a flowchart illustrating the threshold-value comparisonprocessing;

FIG. 12 shows a flowchart representing the correlation-data storageprocessing;

FIG. 13 is a timing diagram showing the timing charts of signals whichappear in the signal receiving apparatus, and

FIG. 14 is a block diagram showing a typical configuration of hardwareof a computer serving as the signal receiving apparatus provided by theembodiments.

DETAILED DESCRIPTION

Embodiments are explained in detail by referring to diagrams as follows.

FIG. 7 is a block diagram showing a typical configuration of a signalreceiving apparatus 21 according to the embodiment.

The signal receiving apparatus 21 shown in the block diagram of FIG. 7employs a correlation-value computation section 22, a control section23, a RAM (Random Access Memory) 24, and a CPU (Central Processing Unit)25.

The correlation-value computation section 22 receives a signal from asignal receiving circuit having an antenna. Both the signal receivingcircuit and the antenna themselves are not shown in the block diagram ofFIG. 7. When the correlation-value computation section 22 receives asignal from the signal receiving circuit, the correlation-valuecomputation section 22 computes a correlation value P representing acorrelation between a synchronization signal included in the receivedsignal and a synchronization signal determined in advance and suppliesthe correlation value P to the control section 23. As thesynchronization signal determined in advance, the correlation-valuecomputation section 22 has a preregistered series of known symbols to becompared with a synchronization signal inserted into a signal receivedfrom a signal transmitting apparatus not shown in the diagram of FIG. 7.For each received signal, the correlation-value computation section 22computes the correlation value P representing a correlation between thesynchronization signal inserted into the received signal and thepreregistered series of known symbols while sliding the series of knownsymbols over the received signal for every symbol included in thesynchronization signal inserted into the received signal.

The control section 23 receives a correlation threshold value th as apart of initial setting. The correlation threshold value th serves as aboundary condition for typically excluding noises. The control section23 receives a correlation value P from the correlation-value computationsection 22 and stores the correlation value P in the memory 24 byadoption a ring-buffer storage method. The control section 23 alsocompares the correlation value P with the correlation threshold valueth. The operation carried out by the correlation-value computationsection 22 to compute a correlation value P and the operations carriedout by the control section 23 to store the correlation value P in thememory 24 and compare the correlation value P with the correlationthreshold value th are shown in threshold-value comparison processingrepresented by a flowchart shown in FIG. 11. If a correlation value P isfound equal to or greater than the correlation threshold value th, thecontrol section 23 starts correlation-data storage processingrepresented by a flowchart shown in FIG. 12 as processing to acquire andstore remaining correlation data to be used for estimating a channelprofile.

The control section 23 carries out the threshold-value comparisonprocessing and the correlation-data storage processing for each frame ofthe received signal which is composed of a plurality of frames. Thus,the control section 23 carries out the threshold-value comparisonprocessing and the correlation-data storage processing a plurality oftimes. Each time correlation data is acquired and stored in the memory24, the CPU 25 reads out the correlation data from the memory 24.

The memory 24 has N storage locations. The control section 23 stores acorrelation value P (Write data) received from the control section 23 atone of the N storage locations in the memory 24. In addition, inaccordance with control executed by the control section 23, the CPU 25reads out the correlation data (Read data) from the memory 24.

In accordance with an interrupt request received from the controlsection 23, the CPU 25 interrupts the control section 23 to read outcorrelation data from the memory 24 for every frame. Then, the CPU 25computes an average of correlation values P each included in correlationdata read out for one of a plurality of frames in order to estimate achannel profile.

FIG. 8 shows a flowchart representing the threshold-value comparisonprocessing and the correlation-data storage processing which are carriedout by the signal receiving apparatus 21 shown in the block diagram ofFIG. 7.

For example, the signal receiving apparatus 21 receives a signal from asignal transmitting apparatus shown in none of the diagrams of thefigures and starts processing to decode the received signal. Theprocessing represented by the flowchart shown in FIG. 8 begins with astep S11 at which the threshold-value comparison processing is carriedout. In the threshold-value comparison processing, the correlation-valuecomputation section 22 computes a correlation value P and supplies thecorrelation value P to the control section 23. The control section 23receives the correlation value P from the correlation-value computationsection 22 and stores the correlation value P in the memory 24 byadoption a ring-buffer storage method. The control section 23 comparesthe correlation value P with the correlation threshold value th. If thecomparison result produced by the control section 23 in thethreshold-value comparison processing indicates that the correlationvalue P is equal to or greater than the correlation threshold value th,the flow of the processing goes on from the step S11 to a step S12.

At the step S12, the control section 23 carries out the correlation-datastorage processing in accordance with the flowchart shown in FIG. 12. Inthe correlation-data storage processing, the correlation data is storedin the memory 24 at remaining storage locations of the N storagelocations typically centered at a storage location used for storing thecorrelation value P computed for the principal wave of the receivedsignal. Then, the correlation-data storage processing is ended.

FIG. 9 is a diagram referred to in description of the threshold-valuecomparison processing carried out at the step S11 of the flowchart shownin FIG. 8.

As shown in the diagram of FIG. 9, the memory 24 is composed of Nstorage locations given storage addresses Address_0 to Address_N−1respectively. In the threshold-value comparison processing and thecorrelation-data storage processing, a correlation value P is stored inone of the N storage locations of the memory 24. Typically, the firstcorrelation value P is stored at the head storage location given thefirst address Address_0. Thereafter, subsequent correlation values P arestored at following storage locations given storage addresses Address_1to Address_N−1 respectively. As a correlation value P is stored at thetail storage location given the last address Address_N−1, the nextcorrelation value P is stored again at the head storage location giventhe first address Address_0. This technique to store correlation valuesP is so-called ring-buffer storage method.

FIG. 10 is a plurality of diagrams each showing a storage image of the Nstorage locations in the memory 24 during the correlation-data storageprocessing carried out at the step S12 of the flowchart shown in FIG. 8.

To be more specific, FIG. 10A is a diagram showing a storage image ofthe N storage locations of the memory 24 in which the address Address_mused for storing, the correlation value P of the principal wave is inthe upper half of the N storage locations of the memory 24, that is,m≦N/2. On the other hand, FIG. 10B is a diagram showing a storage imageof the N storage locations of the memory 24 in which the addressAddress_m used for storing the correlation value P of the principal waveis in the lower half of the N storage locations of the memory 24, thatis, m>N/2.

In the correlation-data storage processing, correlation values Pcomputed after detection of the correlation value P of the principalwave are stored in a later half portion of the N storage locations inthe memory 24. In the case of the typical example shown in the diagramof FIG. 10A, the later half portion of the N storage locations in thememory 24 ends at Address_m+N/2 whereas, in the case of the typicalexample shown in the diagram of FIG. 10B, the later half portion of theN storage locations in the memory 24 ends at Address_N-m+N/2). Theearlier half portion of the N storage locations in the memory 24 is usedfor storing correlation values P computed prior to the detection of thecorrelation value P of the principal wave.

That is to say, since the control section 23 stores the correlationvalue P in the memory 24 by adoption a ring-buffer storage method, ataddresses lower than an address at which the correlation value P of theprincipal wave is stored, a correlation value P computed before thecorrelation value P of the principal wave is computed is stored. Thus,at the N storage locations, correlation values P composing thecorrelation data are stored with the correlation value P of theprincipal wave occupying about the center of the N storage locations.

Next, the threshold-value comparison processing carried out at the stepS11 of the flowchart shown in FIG. 8 is explained by referring to theflowchart shown in FIG. 11.

The flowchart shown in FIG. 11 begins with a step S21 at which thecorrelation-value computation section 22 receives a signal from a signalreceiving circuit having an antenna, not shown, and computes acorrelation value P representing a correlation between a synchronizationsignal supplies the correlation value P to the control section 23. Whenthe process of the step S21 is carried out for the first time by thecorrelation-value computation section 22, the head symbol series of thereceived signal supplied by the signal receiving circuit is taken as thesubject of processing to compute a correlation value P. When the processof the step S21 is carried out, on the other hand, the symbol series ofthe received signal is sled by one symbol from the symbol series used inthe computation of a correlation value P for the first time. When theprocess of the step S21 is carried out for the third time, the symbolseries of the received signal is sled by one symbol from the symbolseries used in the computation of a correlation value P for the secondtime, and so on. That is, when the process of the step S21 is carriedout, a specific symbol series of the present received signal is used asthe subject of processing to compute a correlation value P representinga correlation between the specific symbol series and the known symbolseries of the synchronization signal. In this case, the specific symbolseries of the received signal is obtained by sliding the symbol seriesused in the computation of a correlation value P of the received signalimmediately preceding the present received signal by 1 symbol.

After the process of the step S21 has been completed, the flow of thethreshold-value comparison processing goes on to a step S22 at which thecontrol section 23 stores the correlation value P computed by thecorrelation-value computation section 22 at the step S21 at apredetermined address in the memory 24. When the process of the step S22is carried out for the first time by the control section 23, the controlsection 23 stores the correlation value P at a head address, i.e.,Address_0 in the memory 24. Then, the flow of the threshold-valuecomparison processing goes on to a step S23.

At the step S23, the control section 23 compares the correlation value Pstored in the memory 24 at the step S22 with a correlation thresholdvalue th in order to produce a result of determination as to whether ornot the correlation value P is greater than the correlation thresholdvalue th (i.e., P>th).

If the comparison result produced by the control section 23 at the stepS23 indicates that the correlation value P stored in the memory 24 atthe step S22 is not greater than the correlation threshold value th, theflow of the threshold-value comparison processing goes on to a step S24.At the step S24, the control section 23 increments the address, at whichthe correlation value P is to be stored in the memory 24 at the stepS22, by 1. That is to say, the control section 23 makes use of the nextaddress following the address already used for storing the correlationvalue P at the step S22 as an address to be used for storing thecorrelation value P in the next execution of the process of the stepS22. Then, the flow of the threshold-value comparison processing goesback to the step S21 to repeat the processes of the steps S21, S22 andS23. As a result, correlation values P are stored in the memory 24 byadoption of the ring buffer technique explained earlier by referring tothe diagram of FIG. 9.

If the comparison result produced by the control section 23 at the stepS23 indicates that the correlation value P is greater than thecorrelation threshold value th, on the other hand, the threshold-valuecomparison processing is ended.

As described earlier by referring to the flowchart shown in FIG. 8,after the threshold-value comparison processing of the step S11 has beencompleted, the correlation-data storage processing is carried out at thestep S12.

FIG. 12 shows a flowchart representing the correlation-data storageprocessing carried out at the step S12 of the flowchart shown in FIG. 8.

The flowchart shown in FIG. 8 begins with a step S31 at which thecontrol section 23 initializes a variety of parameters. For example, thecontrol section 23 sets the maximum correlation value max at thecorrelation value P determined to be greater than the correlationthreshold value th at the step S23 of the flowchart shown in FIG. 11.The maximum correlation value max is a parameter representing thelargest correlation value P among correlation values P obtained in thiscorrelation-data storage processing. As another example, the controlsection 23 also sets a stored-data count num at 0. The stored-data countnum is a parameter representing the number of correlation values P whichare computed and stored in the memory 24 after the correlation value Pdetermined to be equal to the maximum correlation value max has beenstored in the memory 24. The correlation values P includes thecorrelation value P determined to be equal to the maximum correlationvalue max.

After the process of the step S31 has been completed, the flow of thecorrelation-data storage processing goes on to a step S32 at which thecontrol section 23 increments the address, at which the correlationvalue P is to be stored in the memory 24 at a step S36 to be describedlater, by 1 to serve as the following address used for storing the nextcorrelation value P. The address to be incremented by 1 by the controlsection 23 by carrying out the process at the step S32 is an addressused last to store a correlation value P at the step S22 of theflowchart shown in FIG. 11 or an address used to store a correlationvalue P at the step S36 executed in an immediately preceding loop of thecorrelation-data storage processing. After the process of the step S32has been completed, the flow of the correlation-data storage processinggoes on to a step S33.

At the step S33, the control section 23 increments the stored-data countnum by 1. After the process of the step S33 has been completed, the flowof the correlation-data storage processing goes on to a step S34.

At the step S34, the control section 23 produces a result ofdetermination as to whether or not the stored-data count num incrementedby 1 at the immediately preceding step S33 is greater than half thememory size set at N storage locations as the size of the memory 24(that is, num>N/2). That is to say, the control section 23 produces aresult of determination as to whether or not N/2 correlation values Phave been stored in the memory 24 since the operation to store thecorrelation value P determined to be equal to the maximum correlationvalue max in the memory 24. Initially, the correlation value Pdetermined to be equal to the maximum correlation value max in thememory 24 has been stored at the step S22 of the flowchart shown in FIG.11. That is to say, the initial maximum correlation value max is thecorrelation value P which has been stored at the step S22 of theflowchart shown in FIG. 11.

If the determination result produced by the control section 23 at thestep S34 indicates that the stored-data count num is not greater thanhalf the memory size set at N storage locations as the size of thememory 24, that is, if the determination result produced by the controlsection 23 at the step S34 indicates that the number of correlationvalues P which have been stored in the memory 24 since the operation tostore the correlation value P determined to be equal to the maximumcorrelation value max in the memory 24 is not greater than N/2, the flowof the correlation-data storage processing goes on to a step S35 atwhich the correlation-value computation section 22 computes thecorrelation value P representing a correlation between the symbol seriesin the received signal and the symbol series in the synchronizationsignal in the same way as the process carried out at the step S21 of theflowchart shown in FIG. 11 and supplies the correlation value P to thecontrol section 23. In the same way as the process carried out at thestep S21, the process of the step S21 is carried out by thecorrelation-value computation section 22 by making use of a specificsymbol series of the present received signal as the subject ofprocessing to compute a correlation value P representing a correlationbetween the specific symbol series and the symbol series of thesynchronization signal. In this case, the specific symbol series of thereceived signal is obtained by sliding the symbol series used in thecomputation of a correlation value P of the received signal immediatelypreceding the present received signal by 1 symbol.

After the process of the step S35 has been completed, the flow of thecorrelation-data storage processing goes on to a step S36 at which, inthe same way as the process carried out at the step S22 of the flowchartshown in FIG. 11, the control section 23 stores the correlation value Pcomputed by the correlation-value computation section 22 at the step S35at an address set at the step S32 as an address in the memory 24. Afterthe process of the step S36 has been completed, the flow of thecorrelation-data storage processing goes on to a step S37.

At the step S37, the control section 23 compares the correlation value Pcomputed at the step S35 with the maximum correlation value max set atthe step S31 in order to produce a result of determination as to whetheror not the correlation value P is greater than the maximum correlationvalue max (that is, P>max).

If the determination result produced by the control section 23 at thestep S37 indicates that the correlation value P is not greater than themaximum correlation value max, that is, if the result of thedetermination indicates that the correlation value P is smaller than themaximum correlation value max, the flow of the correlation-data storageprocessing goes back to the step S32 to repeat the processes describedabove, starting with the process of the step S32.

If the determination result produced by the control section 23 at thestep S37 indicates that the correlation value P is greater than themaximum correlation value max, on the other hand, the flow of thecorrelation-data storage processing goes back to the step S31 to repeatthe processes described above, starting with the process of the stepS31. It is to be noted, however, that at the step S31 carried out thistime, the maximum correlation value max is updated to the correlationvalue P determined at the step S37 to be greater than the currentmaximum correlation value max and the stored-data count num is againreset at 0.

As described above, correlation values P are stored in the memory 24 bycarrying out the correlation-data storage processing repeatedly. As thedetermination result produced by the control section 23 at the step S34indicates that the stored-data count num is greater than half the memorysize set at N storage locations as the size of the memory 24, thecorrelation-data storage processing is ended. As described above, afterthe correlation value P determined to be equal to the maximumcorrelation value max has been stored in the memory 24, N/2 correlationvalues P forming the second half part of the correlation data are storedin the memory 24. As described above, the integer N representing thestorage capacity of the memory 24 is the number of storage locations inthe memory 24. In addition, since correlation values P are stored in thememory 24 by adoption of the ring-buffer method, before the correlationvalue P determined to be equal to the maximum correlation value max isstored in the memory 24, N/2 correlation values P forming the first halfpart of the correlation data have been stored in the memory 24. That isto say, correlation values P forming correlation data are stored in thememory 24 at N storage locations centered at an address used for storingthe correlation value P determined to be equal to the maximumcorrelation value max.

In general, the correlation value P representing a correlation with thesynchronization signal included in the principal wave is the largestcorrelation value P among the correlation values P forming correlationdata stored in the memory 24. The largest correlation value P among thecorrelation values P forming correlation data stored in the memory 24 isreferred to as the maximum correlation value max. Thus, the signalreceiving apparatus 21 is capable of storing the correlation values Pforming correlation data in the memory 24 at N storage locationscentered at an address used for storing the correlation value Prepresenting a correlation with the synchronization signal included inthe principal wave. In other words, the signal receiving apparatus 21 iscapable of storing the N/2 correlation values P on the upstream side ofthe correlation value P representing a correlation with thesynchronization signal included in the principal wave and the N/2correlation values P on the downstream side of the correlation value Prepresenting a correlation with the synchronization signal included inthe principal wave in the memory 24.

As described above, the signal receiving apparatus 21 is capable ofstoring the correlation values P forming correlation data in the memory24 at N storage locations centered at an address used for storing thecorrelation value P representing a correlation with the synchronizationsignal included in the principal wave. Thus, the CPU 25 is capable ofestimating a proper channel profile from correlation data acquired for aplurality of frames. The proper channel profile estimated in this way isa channel profile estimated from correlation data including thecorrelation values P of a principal wave, a pre-echo and a post-echo.

That is to day, if the operation to store correlation data starts withan operation to store the correlation value P of a principal wave asexplained earlier by referring to the diagram of FIG. 5 for example, thecorrelation data will not include the correlation value P of a pre-echo.Since the signal receiving apparatus 21 stores the correlation values Pforming correlation data in the memory 24 at N storage locationscentered at an address used for storing the correlation value Pdetermined to be equal to the maximum correlation value max as describedabove, the correlation value P of a pre-echo is included in the storedcorrelation data with a high degree of reliability.

In addition, as explained earlier by referring to the diagram of FIG. 6,if the correlation threshold value th is set at too a low level, thecorrelation value P of a post echo cannot be stored in the memory 24 insome cases. On the basis of a result of comparing a correlation value Pwith the maximum correlation value max, the signal receiving apparatus21 is capable of storing the correlation values P forming correlationdata in the memory 24 at N storage locations centered at an address usedfor storing the correlation value P determined to be equal to themaximum correlation value max as described above by referring theflowchart shown in FIG. 12. Thus, it is possible to prevent theoperation to store correlation values P from being started by a noiseused as a trigger. As a result, the correlation value P of the post-echois included in the stored correlation data with a high degree ofreliability.

In the embodiment described above, the signal receiving apparatus 21 iscapable of storing the correlation values P forming correlation data inthe memory 24 at N storage locations centered at an address used forstoring the correlation value P representing a correlation with thesynchronization signal included in the principal wave. It is to benoted, however, that the address used for storing the correlation valueP representing a correlation with the synchronization signal included inthe principal wave can also be an address lagging behind the startaddress of the memory 24 used for storing the correlation data by atypical distance of N/3 or 2N/3 storage locations. That is to say, thenumber of correlation values P to be stored in the memory 24 to form thelater part of the correlation data after the correlation value Pdetermined to be equal to the maximum correlation value max has beenstored in the memory 24 does not have to be N/2. Instead, the number ofcorrelation values P to be stored in the memory 24 to form the laterpart of the correlation data after the correlation value P determined tobe equal to the maximum correlation value max has been stored in thememory 24 can be a typical value of 2N/3 or N/3. It is to be noted thatthe number of correlation values P stored in the memory 24 is the numberof symbols stored in the memory 24.

In addition, by setting the integer N representing the size of thememory 24 at a large value, the signal receiving apparatus 21 is capableof coping with echos in a broader range.

The synchronization signal is inserted into every frame in a signaltransmitted through a transmission line by a signal transmittingapparatus shown in none of the diagrams of the figures as a frame havinga frame length determined in advance and the signal receiving apparatus21 acquires correlation data for a plurality of such frames. Then, thesignal receiving apparatus 21 estimates a channel profile representingthe characteristic of the transmission line by taking an average ofpieces of such correlation data.

By referring to a diagram of FIG. 13, the following description explainsprocessing to write correlation data into the memory 24 and processingto read out correlation data from the memory 24 a plurality of times inaccordance with interrupts made by the CPU 25. In the case of thetypical example explained by referring to the diagram of FIG. 13, theprocessing to write correlation data into the memory 24 and theprocessing to read out correlation data into the memory 24 are carriedout 2 times for 2 successive frames respectively. In the followingdescription, the 2 consecutive frames are referred to as first andsecond frames.

FIG. 13 is a timing diagram showing the timing charts of signals whichappear in the signal receiving apparatus 21.

The first (or top) timing chart of the timing diagram of FIG. 13 is thetiming chart of a correlation value P computed by the correlation-valuecomputation section 22. The second timing chart is the timing chart of awrite-permit signal for allowing the control section 23 to store thecorrelation value P in the memory 24. The third timing chart is thetiming chart of an operation to store the correlation value P of thecorrelation data into the memory 24. In the timing diagram, thecorrelation values P forming the correlation data are denoted by symbolsd₀ to d_(N-1). The fourth timing chart is the timing chart of aread-permit signal for allowing the CPU 25 to read out a correlationvalue P from the memory 24. The fifth (or bottom) timing chart is thetiming chart of an operation to read out the correlation value P of thecorrelation data from the memory 24. As described above, the correlationvalues P forming the correlation data are denoted by symbols d₀ tod_(N-1).

First of all, for the first frame, by carrying out the threshold-valuecomparison processing represented by the flowchart shown in FIG. 11 andthe correlation-data storage processing represented by the flowchartshown in FIG. 12, the control section 23 stores the correlation values Pforming correlation data in the memory 24 at N storage locationscentered at an address used for storing the correlation value P. Afterthe control section 23 completes the correlation-data storage processingto store the correlation values P, the control section 23 issues arequest for an interrupt to the CPU 25. In response to the request foran interrupt, the CPU 25 makes an interrupt. In this case, the interruptmade by the CPU 25 is an interrupt to read out a correlation value Pfrom the memory 24.

As described above, when the control section 23 issues a request for aninterrupt to the CPU 25, the CPU 25 makes an interrupt in response tothe request for an interrupt. Interrupted by the CPU 25, the controlsection 23 supplies the read-permit signal and a read address to thememory 24 in order to enable the memory 24 to output the correlationdata denoted by symbols d₀ to d_(N-1), to the CPU 25 as read data.

Thereafter, the control section 23 starts the write processing for thesecond frame in accordance with a self-running counter embedded in thecontrol section 23. The control section 23 supplies the write-permitsignal, a write address and a correlation value P computed by thecorrelation-value computation section 22 to the memory 24 in order toenable the memory 24 to store the correlation value P at the writeaddress as write data. At a point of time the control section 23completes the correlation-data storage processing to store thecorrelation values P, the control section 23 issues a request for aninterrupt to the CPU 25. In this way, the control section 23 carries outan operation to write correlation data into the memory 24 and anoperation to drive the CPU 25 to read out correlation data from thememory 24 for every frame of the received signal.

Then, the CPU 25 computes an average of correlation values P eachincluded in correlation data read out from the memory 24 for one of aplurality of frames in order to estimate a channel profile. In the caseof the typical frames shown in the timing diagram of FIG. 13 forexample, the CPU 25 computes the average of the correlation valuedenoted by symbol d₀ as a correlation value P computed for the firstframe and the correlation value denoted by symbol d′₀ as a correlationvalue P computed for the second frame. Then, the CPU 25 computes theaverage of the correlation value denoted by symbol d₁ as a correlationvalue P computed for the first frame and the correlation value denotedby symbol d′₁ as a correlation value P computed for the second frame.This operation to compute an average value is carried out for everycouple of correlation values P computed for the first and second framesrespectively till the execution of the operation to compute the averageof the correlation value denoted by symbol d_(N-1) as a correlationvalue P computed for the first frame and the correlation value denotedby symbol d′_(N-1) as a correlation value P computed for the secondframe in order to estimate a channel profile representing the averagescomputed for the correlation values d₀ to d_(N-1) and the correlationvalues d′₀ to d′_(N-1).

By computing averages for a plurality of pieces of correlation data asdescribed above, the effects of noises can be reduced. As a result, amore accurate channel profile can be estimated.

It is to be noted that the embodiments can be applied to not only asignal receiving apparatus for receiving digital broadcasts, but alsoother apparatus such as a relay apparatus installed at a relay stationto serve as an apparatus for relaying digital broadcasts and aradio-communication apparatus such as a portable terminal for carryingout radio communications.

The series of processes described previously can be carried out byhardware and/or execution of software. If the series of processesdescribed above is carried out by execution of software, a variety ofprograms composing the software can be installed into a computerembedded in dedicated hardware, a general-purpose personal computer orthe like from typically a network or a removable recording medium. Inthis case, the computer or the personal computer serves as the signalreceiving apparatus 21 described above. A general-purpose personalcomputer is a personal computer, which can be made capable of carryingout a variety of functions by installing a variety of programs into thepersonal computer.

FIG. 14 is a block diagram showing a typical configuration of hardwareof a microcomputer which serves as the computer (or the personalcomputer) for executing the programs in order to carry out the series ofprocesses described above.

The programs can be stored in advance in an EEPROM (ElectricallyErasable Programmable Read-only Memory) 105 or a ROM 103. Each of theEEPROM 105 and the ROM 103 is a storage medium embedded in themicrocomputer.

As an alternative, the aforementioned removable recording medium fortemporarily or permanently storing (or recording) the programs to beinstalled into the microcomputer shown in the diagram of FIG. 14 asprograms to be executed by the microcomputer is provided to the userseparately from the main unit of the microcomputer. Examples of theremovable recording mediums also each referred to as a package mediuminclude a magnetic disk such as a flexible disk, an optical disk such asa CD-ROM (Compact Disk-Read Only Memory) or a DVD (Digital VersatileDisk), an MO (Magneto-Optical) disk such as an MD (Mini Disk) as well asa semiconductor memory.

Instead of installing the programs into the microcomputer from theremovable recording mediums, the programs can also be downloaded from aprogram provider external to the microcomputer by way of a radio and/orwire network. In the microcomputer, the programs are received by aninput/output interface 110 and installed in the EEPROM 105 embedded inthe microcomputer.

As shown in the block diagram of FIG. 14, the microcomputer employs aCPU (Central Processing Unit) 102, a ROM (Read Only Memory) 103, a RAM(Random Access Memory) 104, the EEPROM 105 and the input/outputinterface 110 which are connected to each other by a bus 101. In placeof the CPU 102, a DSP (Digital Signal Processor) can also be used.

The CPU 102 is a section for executing the programs after the programshave been loaded into the RAM 104. Each of the programs loaded into theRAM 104 can be a program stored in advance in the ROM 103 or a program,which has been installed in the EEPROM 105 from an aforementionedremovable recording medium or from the program provider cited above. TheCPU 102 executes the programs in order to carry out each series ofprocesses represented by one of the flowcharts explained previouslyand/or processes of blocks shown in the block diagram of FIG. 7. It isto be noted that the CPU 102 exchanges data with apparatus external tothe microcomputer by way of the input/output interface 110.

It is also to be noted that each program to be executed by themicrocomputer can be a program executed for carrying out processes alongthe time axis in an order explained in this specification or a programexecuted for carrying out processes concurrently or with requiredtimings such as an invocation timing.

It is also worth noting that, in this specification, steps of eachflowchart described above can be carried out to perform processes notonly in a pre-prescribed order along the time axis, but alsoconcurrently or individually. Typical examples of the processes carriedout concurrently or individually are parallel processes andobject-oriented processes. In addition, a program can be executed by notonly 1 CPU, but also a plurality of CPUs in the so-called distributedprocessing.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. A signal receiving apparatus for receiving signals, said signalreceiving apparatus comprising: a correlation-value computation sectionconfigured to sequentially compute a correlation value representing acorrelation between a received signal and a series of known symbolswhile sliding said series of known symbols for every symbol included insaid received signal; a maximum-value detection section configured todetect a largest correlation value among said correlation valuescomputed by said correlation-value computation section for one frame ofsaid received signal; and a correlation-value storage section configuredto store each of the correlation values at one of a predetermined numberof storage locations, before and after said largest correlation value isdetected by said maximum-value detection section.
 2. The signalreceiving apparatus according to claim 1 wherein: said correlation-valuestorage section is used for storing as many correlation values for eachof frames of said received signal as the predetermined number of storagelocations; and a channel-profile estimation section further included insaid signal receiving apparatus is used for estimating a channel profilerepresenting characteristics of a transmission line used fortransmitting said signal to said signal receiving apparatus on the basisof every average of corresponding correlation values each computed forone of a plurality of said frames.
 3. The signal receiving apparatusaccording to claim 1, said signal receiving apparatus further comprisinga correlation-value detection section configured to compare each of saidcorrelation values computed by said correlation-value computationsection with a threshold value determined in advance in order to detecta correlation value greater than said threshold value, wherein saidcorrelation-value storage section is used for storing each of saidcorrelation values by adoption of a ring-buffer method until saidcorrelation-value detection section detects a correlation value that isgreater than said threshold value.
 4. The signal receiving apparatusaccording to claim 3, said signal receiving apparatus furthercomprising: a maximum-value setting section configured to set a maximumcorrelation value at a correlation value detected by saidcorrelation-value detection section as a correlation value greater thansaid threshold value; a maximum-value determination section configuredto produce a result of a determination as to whether or not acorrelation value, which is computed by said correlation-valuecomputation section after said correlation-value detection section hasdetected a correlation value greater than said threshold value, isgreater than said maximum correlation value; and a maximum-valueupdating section configured to update said maximum correlation valuewith a specific correction value determined by said maximum-valuedetermination section to be greater than said maximum correlation valueif said determination result produced by said maximum-valuedetermination section indicates that said specific correlation value isgreater than said maximum correlation value.
 5. A signal receivingmethod for receiving a signal, said signal receiving method comprising:sequentially computing a correlation value representing a correlationbetween a received signal and a series of known symbols while slidingsaid series of known symbols for every symbol included in said receivedsignal, detecting a largest correlation value among said correlationvalues computed at said correlation-value computation step for one frameof said received signal; and storing each of said correlation valuescomputed at said correlation-value computation step at one of apredetermined number of storage locations, before and after said largestcorrelation value is detected at said maximum-value detection step.
 6. Asignal receiving computer program product stored on a computer-readablemedium including executable instructions that when executed by aprocessor embedded in a signal receiving apparatus for receiving signalsperform steps comprising: computing a correlation value representing acorrelation between a received signal and a series of known symbolswhile sliding said series of known symbols for every symbol included insaid received signal, detecting a largest correlation value among saidcorrelation values computed in said correlation-value computationprocess for one frame of said received signal; and storing each of saidcorrelation values computed in said correlation-value computationprocess at one of a predetermined number of storage locations, beforeand after said largest correlation value is detected in saidmaximum-value detection process.
 7. A signal receiving apparatus forreceiving signals, said signal receiving apparatus comprising:correlation-value computation means for sequentially computing acorrelation value representing a correlation between a received signaland a series of known symbols while sliding said series of known symbolsfor every symbol included in said received signal; maximum-valuedetection means for detecting a largest correlation value among saidcorrelation values computed by said correlation-value computation meansfor one frame of said received signal; and correlation-value storagemeans for storing each of the correlation values at one of apredetermined number of storage locations, before and after said largestcorrelation value is detected by said maximum-value detection means.